One expensive option would be for individual owners to install bollards in their own parking spaces and issue keys to whoever they wish to permit to park in those spaces. If that requires a resolution of a general meeting to permit an owner to install a bollard in their own parking space (I don’t know if it does), and if people want to take that route, you could quietly assemble a group of owners that amounts to a majority to agree that they will support the motion. The owners who support the motion could then all propose it together so no-one is identified as a ring-leader.
If you decide that no motion is required to install a bollard on a parking space that is within your own title area then you could arrange for a ‘bulk-buy’ all at once so you can get it done less expensively due to the economy of scale. Once you know a majority are on board, the ‘group’ could offer it to all owners, including the miscreant. That would be absolutely fair, transparent and without bias. How could he object?